Re: [PATCH] x86/perf/intel/cqm: Get rid of the silly for_each_cpu lookups

[Vikas Shivappa]

On Wed, 17 Feb 2016, Thomas Gleixner wrote:

On Wed, 17 Feb 2016, Thomas Gleixner wrote:

CQM is a strict per package facility. Use the proper cpumasks to lookup the
readers.

Sorry for the noise. PEBKAC: quilt refresh missing. Correct version below.

Thanks,

        tglx

8<----------

Subject: x86/perf/cqm: Get rid of the silly for_each_cpu lookups
From: Thomas Gleixner <t...@linutronix.de>
Date: Sun, 14 Feb 2016 23:09:06 +0100

CQM is a strict per package facility. Use the proper cpumasks to lookup the
readers.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
arch/x86/kernel/cpu/perf_event_intel_cqm.c |   34 ++++++++++-------------------
1 file changed, 12 insertions(+), 22 deletions(-)

--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -1244,15 +1244,12 @@ static struct pmu intel_cqm_pmu = {

static inline void cqm_pick_event_reader(int cpu)
{
-       int phys_id = topology_physical_package_id(cpu);
-       int i;
+       int reader;

-       for_each_cpu(i, &cqm_cpumask) {
-               if (phys_id == topology_physical_package_id(i))
-                       return; /* already got reader for this socket */
-       }
-
-       cpumask_set_cpu(cpu, &cqm_cpumask);
+       /* First online cpu in package becomes the reader */
+       reader = cpumask_any_and(topology_core_cpumask(cpu), &cqm_cpumask);
+       if (reader >= nr_cpu_ids)
+               cpumask_set_cpu(cpu, &cqm_cpumask);

I was confused by the topology_core_cpumask naming as its really the mask of all 
cpus in the same package. I sent a patch for cqm and rapl to fix this looping 
when you had given the same feedback during CAt patches review , 
but they have never made it so far due to CAT patch issues.

Would it be better to resend the rapl (looks like perf_uncore has same loop) 
fixes separately ?

Thanks,
Vikas

}

static void intel_cqm_cpu_starting(unsigned int cpu)
@@ -1270,24 +1267,17 @@ static void intel_cqm_cpu_starting(unsig

static void intel_cqm_cpu_exit(unsigned int cpu)
{
-       int phys_id = topology_physical_package_id(cpu);
-       int i;
+       int target;

-       /*
-        * Is @cpu a designated cqm reader?
-        */
+       /* Is @cpu the current cqm reader for this package ? */
        if (!cpumask_test_and_clear_cpu(cpu, &cqm_cpumask))
                return;

-       for_each_online_cpu(i) {
-               if (i == cpu)
-                       continue;
-
-               if (phys_id == topology_physical_package_id(i)) {
-                       cpumask_set_cpu(i, &cqm_cpumask);
-                       break;
-               }
-       }
+       /* Find another online reader in this package */
+       target = cpumask_any_but(topology_core_cpumask(cpu), cpu);
+
+       if (target < nr_cpu_ids)
+               cpumask_set_cpu(target, &cqm_cpumask);
}

static int intel_cqm_cpu_notifier(struct notifier_block *nb,